A lot of people seem to like this business of being pseudonymous, and nobody knowing who you are or anything about you unless you tell them.
I suppose if you are famous or notorious that might appeal. "If they knew I weas reallynthe Oope they'd get all embarassed and I couldn't post on the Improper Language thread..." - that kmind of stuff.
But otherwise I can't see the point. I'd sooner be out in the open, so long as noone's shooting at me. Even did a profile.